The present invention relates to a drive device configured for attachment to a drive spindle of a power tool, for example a hand drill, and more particularly to a portable tool driver incorporating an impact drive mechanism.
The benefits of impact drive mechanisms are well understood by those skilled in the art. For example, impact drive mechanisms are conventionally incorporated into impact air wrenches and conventional hammer drills. These mechanisms add the additional benefit of a hammering effect to conventional rotational drives.
However, a drawback of conventional impact drive mechanisms is that such devices are typically only incorporated directly into the drive device of the drill or power tool. In other words, the entire tool constitutes the impact drive mechanism, and there are certain situations wherein an impact drive is not desired. Additionally, the impact drive mechanisms of the known conventional devices are relatively sophisticated and expensive to manufacture.
U.S. Pat. No. 4,840,387 to McCarthy describes a keyless chuck device for attachment to a drive spindle of a drill in which the operating sleeve has impact members biased toward mating impact members associated with the rotatable nut. The impact dogs disclosed in the '387 patent are meant to increase the tightening (or loosening) effect of the chuck device on a tool shank carried therein depending on the direction of rotation of the body of the chuck. The chuck does not impart an impact drive to the tool bit once the chuck is tightened onto the tool bit.